Re: [PATCH v7 1/3] mm/slub: only zero requested size of buffer for kzalloc when debug enabled

[Feng Tang]

On Thu, Nov 10, 2022 at 11:20:34AM +0800, Tang, Feng wrote:
> On Wed, Nov 09, 2022 at 03:28:19PM +0100, Vlastimil Babka wrote:
[...]
> > > +	/*
> > > +	 * For kmalloc object, the allocated memory size(object_size) is likely
> > > +	 * larger than the requested size(orig_size). If redzone check is
> > > +	 * enabled for the extra space, don't zero it, as it will be redzoned
> > > +	 * soon. The redzone operation for this extra space could be seen as a
> > > +	 * replacement of current poisoning under certain debug option, and
> > > +	 * won't break other sanity checks.
> > > +	 */
> > > +	if (kmem_cache_debug_flags(s, SLAB_STORE_USER) &&
> > 
> > Shouldn't we check SLAB_RED_ZONE instead? Otherwise a debugging could be
> > specified so that SLAB_RED_ZONE is set but SLAB_STORE_USER?
> 
> Thanks for the catch!
> 
> I will add check for SLAB_RED_ZONE. The SLAB_STORE_USER is for
> checking whether 'orig_size' field exists. In earlier discussion,
> we make 'orig_size' depend on STORE_USER, https://lore.kernel.org/lkml/1b0fa66c-f855-1c00-e024-b2b823b18678@xxxxxxx/ 

Below is the updated patch, please review, thanks! 

- Feng

-----8>----